In traditional radio networks comprising of basestation(s) and passive antenna systems, there is at least one connectorised 50Ω port on the antenna and at least one connectorised 50Ω port on the basestation that allows signals to be passed there between via at least one 50Ω connectorised cable. The connectors on the base station could be, for example, 7/16 DIN RF connectors or N-type RF connectors. The connectorised 50Ω base station and antenna port(s) can also be used as one or more test port(s), to facilitate test and power calibration of radio frequency (RF) transceiver circuit(s) of the basestation. Advantageously, connectorised 50Ω port(s) used to allow interconnect to antenna can instead be coupled to test equipment to allow measurements to be performed on the signals coupled there between.
FIG. 1 illustrates simplified block diagrams of a traditional base station with an antenna (array) in a transmit 100 and receive 150 configuration. Referring first to the transmit configuration 100, a passive antenna 108 is coupled to a transmit filter 106 via a 50Ω connectorised cable 107. The transmit filter 106 is further coupled to an optional external power amplifier module 104, which, in turn, is coupled to a base station cabinet module 102 via a further 50Ω connector 103. In this manner, the 50Ω connectors 103 and 107 that couple the base station cabinet module 102 to the passive antenna 108 may be utilised as test ports, to allow the transmitter to be tested and calibrated. Optionally the base station cabinet may include the transmit (TX) filter module, 106 and the power amplifier module, 104. Referring now to the receive configuration 150, passive antenna 108 is coupled to a receive filter 156 via a 50Ω connectorised cable 157. The receive filter 156 is further coupled to an external low noise amplifier module 154 that is, in turn, coupled to a base station cabinet module 102 via a further 50Ω connector 153.
As in the transmit configuration the receive (RX) filter 156 and LNA 154 maybe integrated as part of the basestation cabinet 102, As discussed above, the 50Ω connectors 153 and 157 may be utilised as test ports, to allow the receiver to be tested and calibrated. Routinely, the connectorised cable 107 used for transmit testing and the connectorised cable 157 used for receive testing are the same cable, thereby allowing for the sharing of the antenna and feeder cable for both transmit and receive functions. In this case, the transmit filter 106 and receive filter 156 may be combined in the form of a duplex filter.
FIG. 1 refers to the basestation wireless interface standard specification 3GPP™ TS 25.104 definition of transmit and receive test points for specification and conformance testing. In traditional systems, a connectorised 50Ω connection exists for operational modes. In Active antenna systems (AASs) the individual antenna radiating elements are directly connected to their associated radio base station electronics and are integrated in the same housing. In AAS, there is no operational mode requiring a 50Ω connection that is externally connectable. Therefore, currently, in order to carry out conformance testing, the AAS has to be disassembled or (at least a significant portion) partially disassembled in order to access the individual radiating elements within the housing. Testing units in a disassembled or partially disassembled state inherently affects electromagnetic radiation patterns for antenna measurements and, thus, leads to results that would therefore not be representative of the performance expected if the AAS were fully assembled in a field-deployed system.
Further, any form of disassembly requires breaking environmental and security seals, which would compromise the future functionality of the AAS. Another option may be to perform radiative testing. Far field radiative testing does not require disassembly of the AAS, but does require an anechoic chamber. Anechoic chambers are physically large enclosed spaces where the external ambient radiation from commercial RF services is suppressed. Anechoic chambers also suppress interference from the antenna under test (AUT) from radiating to licensed bands in the vicinity of the chamber by being enclosed in a Faraday cage structure. Anechoic chamber walls, floors and ceiling surfaces are covered with RF absorbent conical structures that substantially minimise reflections that could ordinarily impact radiative measurements. The RF absorbent conical structures placed on the inner surfaces of the anechoic chamber help minimise a problem with radiative testing by suppressing multipath signals. Multipath signals would distort, for example, the signal received in a probe antenna measuring an AAS in an anechoic chamber causing a high degree of measurement uncertainty or distorting the results to an indeterminate level.
Further, some AASs can be physically large, and in the case of the 700 MHz to 900 MHz band, the antennas can be in excess of 2 meters high. In the case of a 2 meter high 700 MHz antenna, the far-field can be greater than 55 meters. Therefore, very large anechoic chambers would be required.
In the case of near field testing, the exact physical placement or proximity and orientation of the probe antenna is critical in making accurate measurements, as small changes in the position of the antenna can create many tens of dBs (decibels) difference. The near field probe itself adds a huge degree of uncertainty to the test results and the performance of the probe directly impacts the test results. Further, the near field probe is not suitable for many measurements, such as error vector magnitude (EVM), as the near field combination of signals from multiple sources can distort the signal detected by the probe. Therefore, there can be significant differences between near field, far field and conducted measurements.
Referring now to FIG. 2, a known active antenna system (AAS) 200 is illustrated. The AAS 200 comprises, for example, a Common Public Radio Interface (CPRI) interface 240 for interfacing to a baseband processing unit of a cellular base station, such as a third generation partnership project (3GPP™) evolved NodeB. The cellular base station comprises a baseband processing unit that performs, for example, demodulation and decoding in the receive path and modulation and encoding in the transmit path. The AAS 200 comprises one or more of its own baseband processing circuits 208, which are arranged to perform system control, beamform manipulation and additional signal processing.
The AAS 200 comprises a plurality of parallel transceiver circuits 201, consisting of a transmit module 204 and a receive module 206. Transmit module 204 and receive module 206 within the transceiver 201 are also operably coupled to the antenna arrangement 210, as shown.
In this case, the antenna arrangement 210 comprises an antenna array having a plurality of cross polarised (XPOL) antenna elements employing, for example, both +45° and −45° orthogonal antenna elements, with an independent transmit module 204 and receive module 206 connected to each antenna port.
As discussed, current standards bodies only suggest ‘conductive’ test methods to be performed on the 50Ω (test) port of a basestation or of a passive antenna system. This is not possible for the active antenna module 200 in FIG. 2, as this connection point is incorporated into a sealed unit 202 within the AAS. Therefore, the only way to access active antenna module 200 is to disassemble the AAS and test at each active antenna module and each antenna element feed separately. This is not practical for reasons outlined heretofore for the active antenna module 200 in FIG. 2, as this connection point is incorporated into a sealed unit 202 within the AAS. Therefore, the only known way to access active antenna module 200 is to disassemble the AAS and test each active antenna module and each antenna element feed separately.
Therefore, it may be advantageous to determine an alternative mechanism for determining the operational status, performance and functionality of various components, circuits or modules in an AAS without disassembling the system.